Add a macro to read the package versions

[stefanspringer1]

Motivation

In many circumstances, you might want an executable to know about the package version(s) that was used, so the program can give according infos to the user of the program e.g. in case of an error. This should be possible also for programs being distributed as one single executable file. Because this seems to a common issue, an easy to use solution should exist.

Proposed solution

From https://forums.swift.org/t/inserting-gitinformation-into-source-code/77128:

… there should be e.g. a macro #packageVersions making a (literal) map with the versions as part of the standard library. …

Alternatives considered

You cannot do this with your own macro that reads the Package.resolved file, because reading files is prohibited for a macro because of security reasons. Same issue when calling Git.

From https://forums.swift.org/t/inserting-gitinformation-into-source-code/77128:

Take a look at what Swift Testing does: we create a C/C++ target, define C macros in that target that correspond to the gitInformation fields we care about, then bubble those macros up to Swift.

But this is complicated.

Additional information

No response